1. The installation of the new VIRGO Injection Bench
Paolo La Penna
for the VIRGO collaboration
European Gravitational Observatory

2. Recombined configuration: first half of 2004IB

3. Recycled interferometer: July 2004IB

4. PR reflection inside IMC: frequency noise
Black:
PR misaligned
Red:
PR aligned

5. PR reflection scattering inside IMC
MC scattering (10 ppm)
IMC PR
Cavity effect
(10% fringes)

6. Plane Power Recycling mirror
The old PR was made by two parts: a curved one inside an external cylindrical glass mass (it was a lens, part of the telescope for collimating inside the ITF)
The curved part was fixed to the cylindrical by means of a steel ring and pression screws;
There was evidence of mechanical resonances (drifting in time): problems in locking acquisition and in the future Frequency Stabilization: need of a monolitic mirror
Decided to make it plane (get rid of transverse movements of the beam induced by the suspension displacements)

7. The RFC was more stable than IMC: the AA of the RFC worked quite well
IMC and RFC alignment
ABP OFF
10%
ABP
dismounted
The beam was atomatically aligned on the RFC (fixed below the IB) with ABP
The IMC was partly automatically aligned (feedback only on the MC mirror
The RFC was more stable than IMC:
the AA of the RFC worked quite well
the poor AA of the IMC couldn’t correct the drifts

8. PR reflection: Input Beam Attenuation (temporary solution)
IMC
10% M6
From the laser
To the interferometer
700 mW (10% of the full power)
Reference Cavity

9. The PR feedback inside the IMC (mid of 2004)
Simulations on a lock acquisition technique developed following the LIGO experience
Locking trials with this baseline technique failed (first half of July)
Beam attenuation installed (summer)

10. HR M6 vs attenuated M6
HR M6
(Same y-scale)
R=10% M6 Hz Hz

11. The PR feedback inside the IMC (end of 2004)
Restart of the locking trials with the baseline technique (21st September)
Establishement of theVariable Finesse lock acquisition technique (October)
PR locking acquisition after one month (end of October 2004)
CONFIRMATION OF THE BACKSCATTERING PROBLEM
NEED OF AN OPTICAL ISOLATOR (FARADAY)

12. Resume: why to build a new Injection Bench
The reflection of the light inside the Input Mode Cleaner increased the frequency noise, thus making it impossible to lock the recycling cavity
The use of a Faraday isolator was necessary
There was no way to accomodate a Faraday isolator and respective telescope on the old IB: the bench had to be replaced
In addition to this:
It was decided to replace the curved PR with a plane PR (less coupling with the transverse PR displacement): a short (parabolic) telescope on the IB was necessary
It was decided to change the automatic alignment system of the injection system: separate alignment of the Input Mode Cleaner and Reference Cavity

13. The Faraday isolator was tested in Nice with the 20W laser
How did we proceed
The aforementioned problems were individuated in many data takings (C1-C4)
The mechanical design of the bench was performed using essentially Autocad and Ansys
The optical simulation of the bench was performed using mainly Zemax (simulation of optical aberrations and stray light), and by Optocad
The Faraday isolator was tested in Nice with the 20W laser
The new IB was mounted and prealigned in Class 10 room (after old IB dismounting)
Once prealigned it has been inserted into the tower

14. Upper part layout
Autocad drawing
Optocad drawing

15. Lower (RFC) part layout
Autocad drawing
Optocad drawing

16. Autocad 3-D simulation (example)

17. ANSYS model
Marionette
Reference
Cavity

18. Uy Tx Tz ANSYS simulation Probably Dihedron Susp. Legs Wire30 40 50 60 70 80 90
Probably
Dihedron
Legs
(measured in
september 2005) Uy
Susp.
Wire
couplers Tx Tz

19. Plane PR: Beam simulation with spherical mirrors
Input mirrors
End mirrors

20. Plane PR: Beam simulation with parabolic mirrors
Input mirrors
End mirrors

21. Plane PR: (new) 6 parabolic off-axis telescope
With plane PR: a big magnification is needed,
the telescope has to be short (about 700 mm)
Parabolic mirrors are needed
The computed curvature radius are not off-shelf: custom mirrors (Optical Surface)
IMC: waist 4.9 mm
Condensing telescope
FI: waist 2.65 mm
M5: f= 75 mm
M6: f = 600 mm
Ø  10 cm
to PR: waist=20 mm
d= 675 mm

22. Parabolic telescope mechanical mount
Two open loop picomotors
Three closed loop picomotors
X and Z closed loop translators
Mounts designed by ourselves and
Machined by a workshop close to Virgo
Mounting commercial actuators

23. Alignment of the parabolic telescope (Class 10 room)
Laser

24. Starting conditions: misaligned, mismatched
AUTOCOLLIMATOR

25. 1st autocollimator alignment
REF. MIRROR
AUTOCOLLIMATOR

26. 2nd autocollimator alignment
REF. MIRROR

27. Autocollimators aligned

28. 1st mirror alignment
AUTOCOLLIMATOR
AUTOCOLLIMATOR

29. 1st mount alignment
AUTOCOLLIMATOR
AUTOCOLLIMATOR

30. 2nd mount alignment
AUTOCOLLIMATOR
AUTOCOLLIMATOR

31. 2nd mount alignment
AUTOCOLLIMATOR
AUTOCOLLIMATOR

32. Mirror matching
AUTOCOLLIMATOR
AUTOCOLLIMATOR

33. Focussing
AUTOCOLLIMATOR
AUTOCOLLIMATOR

34. Off-axis
AUTOCOLLIMATOR
AUTOCOLLIMATOR

35. Off-axis
AUTOCOLLIMATOR
AUTOCOLLIMATOR

36. Off-axis
AUTOCOLLIMATOR
AUTOCOLLIMATOR

37. Autocollimation
AUTOCOLLIMATOR
AUTOCOLLIMATOR

38. Beam dumpers: aluminum boxes and buffle-glass plates

39. Beam dumpers and PSDs
PSD
Beam dumpers
PSD
PSD
PSD

40. Resume of the main differences between new and old IB
Different shape and strutcture of the bench (octagonal, larger, M6 grid of holes, …)
Thinner suspension wires
Presence of the Faraday isolator
Presence of a collimating (reducing) telescope between the Input Mode Cleaner (two lenses)
Presence of a short (less than 1-m-long) off-axis parabolic telescope (×8)
Separate alignment of the IMC and the RFC
RFC placed after the IMC (no beam on the RFC when the IMC is not locked): it should make the beam on the RFC more stable
Use of several PSDs to monitor the beam on the bench
Use of larger mirrors
Use of specifically designed beam dumpers

41. Beam diameter  10 mm
Beam diameter  40 mm

42. Actions after the recycling cavity locking
Decision to revise the Injection Bench design (June 2004)
Creation of a group charged to redesign the IB (July 2004)
Choice of the Faraday isolator and simulation of several possible telescopes (autumn 2004)
Decision to install a plane PR (and therefore an off-axis parabolic telescope) (November 2004)
Develope of the IB optical and mechanical design and starting of orders and (first months of 2005)
Arrival of the main part of the components (May 2005)
Arrival of the bench (July 2005)
Arrival (delayed) of the last parabolic mirror (M5, 75 mm focal length) (August 2005)

43. Actions after the recycling cavity locking
Dismounting of the old IB and starting of the mounting of the new IB (September 2005)
Insertion of the new IB into the IB tower (begin of november 2005)
IB suspension tuning (november 2005)
Bench prealignment and local controls tuning (end of November 2005)
Mounting of the plane PR (end of November 2005)
Local control of the bench (December 2005)
Nd:YAG injection and beam alignment (December 2005)
Alignment of the IB optics (now)

44. Brewster dielectric polarizers
Rotator
February 2005

45. Mid September 2005

46. Begin of October 2005

47. Main activities before inserting the bench into the tower
Change of the input flange (larger windows)
Change of the Brewster link (to accomodate a larger beam)
Suspension tuning (filter 0 and 7 blades): the bench is heavier (about 150 kg)
Adjustment of the wires length
Full tuning and balancing of the suspension
Mounting of the coils: close to the center of mass plane (more stable equilibrium of the bench)
Cabling (of coils and bench actuators)

48. Insertion into the tower (begin November)
Detector table

49. Insertion into the tower (begin November)
Detector table

50. Begin of November 2005

51. Now

52. Now

53. Main activities after inserting the bench into the tower
Bench heigth setting: some difficulties with the suspension point motors
Balancing of the bench
Orientation of the bench with an HeNe coming from the MC tower: some difficulties in the filter 7 rotation range
Test of the coils: some problems in the frames interrupting RFC beams
Orientation of the local controls target: quite difficult because the small angular range in its orientation

54. Local controls Beam diameter  10 mm Beam diameter  40 mm
The IB local controls use a target, placed in front of the dihedron,
with reference markers (bench translations) and reflecting HeNe beams (angles)
The setup had not been changed with respect to the old IB
Beam diameter  10 mm
Beam diameter  40 mm

55. Old IB local controls

57. After the realignment of the reference beams and target:
New IB local controls
After the realignment of the reference beams and target:
Closing of the coarse and fine with the old IB correction filters and essentially the same gains (end of November)
Adjustment of the reference spots
Fine alignment of the bench with the MC HeNe (begin of December)
Measurement of the mechanical TF (last week)

58. Preliminary: New TF measurement
(Henrich Heitmann and Paolo Ruggi)

59. Full alignment procedure
After this first alignment in Class 100 room, the bench has been mounted inside the tower.
The dummy dihedron is mounted, the LC target is realigned, the local controls of the bench are restarted.
The IB is aligned using the HeNe coming from the MC tower
The Nd:YAG beam is injected into the bench and aligned until a light spot is visible on the MC mirror
The optics on the bench is realigned using the IB actuators
The true dihedron is reinstalled, the IB is put in vacuum, the IMC aligned and locked
After IMC locking, it should be possible to make the final tuning and alignment using the bench actuators.

60. Next steps
Present status:
The fake dihedron is still mounted on the bench
The Nd:YAG beam (up to 5 W for the moment) has been sent into the bench: some light (with even some interference) is visible at the end of the MC
The optics on the bench are being realigned using the IB actuators: we perform this operation staying inside the tower, with the laminar flux on and the LC closed (they are very robust)
The true dihedron will be reinstalled this week, then the IMC will be aligned (we hope it will be possible in air, in order to be able check the RFC alignment)
the IB will put in vacuum, the IMC aligned and locked
After IMC locking, it should be possible to make the final tuning and alignment using the bench actuators.
The beam will be aligned in the ITF